1. Field of the Invention
The present invention relates to a power semiconductor device used for power control. In particular, the present invention relates to a lateral type power FET using nitride semiconductor, a Schottky Barrier Diode (SBD) and the like.
2. Description of the Related Art
Power semiconductor devices such as switching device and diode are used for power control circuits such as switching mode power supply and inverter circuit. The power semiconductor device requires the following characteristics, that is, high breakdown voltage and low ON resistance. There exists a trade-off relationship determined by device material between breakdown voltage and ON resistance in the power semiconductor device. According to recent technical advance, the low ON resistance close to the limitations of the principal device material, that is, silicon is realized in the power semiconductor device. In order to further reduce the ON resistance, the device material needs to be changed. Such as GaN and AlGaN nitride semiconductors or silicon carbide (SiC), wide band gap semiconductors are used as switching device material. By doing so, it is possible to improve the trade-off relationship determined by the above materials, and to achieve low ON resistance. A HEMT (High Electron Mobility Transistor) using nitride semiconductors such as GaN and AlGaN has been disclosed in the document below. The document is R. Coffie et al, “p-Capped GaN—AlGaN—GaN High Electron Mobility Transistors (HEMTs)”, IEEE ELECTRON DEVICE LETTERS, VOL. 23, No. 10. OCTOBER 2002, page 598-590.
Recently, the study of the power semiconductor device using the wide band gap semiconductor has been frequently made. In the nitride semiconductor such as GaN, low ON resistance has been realized. However, design has not been made taking characteristics peculiar to the power device, that is, avalanche withstand capability into consideration. This is because GaN-based device is designed based on radio frequency (RF) device.
Incidentally, in FETs, a field plate electrode is provided, and thereby, high breakdown voltage is achieved. The above technique has been disclosed in JPN. PAT. APPLN. KOKAI Publication Nos. 5-21793 and example.